The current invention is generally related to a method and a system for correcting distortion aberration in images, and more particularly related to a method and a system for determining coefficients for correcting distortion aberration based upon corresponding portions of partially overlapping images.
An image generated by an optical lens is generally susceptible to distortion or aberration. The distortion aberration of a lens is inherent and roughly defined by a positional or geometric discrepancy between a generated image and a true object. In other words, a certain portion of the image generated by the lens does not reflect an original object. For example, a straight line in the original object is often curved in an image generated by a lens. To further define the distortion aberration, referring to FIG. 1, Y is an object placed before a lens, and xcex8 is an incoming angle of the object Y. yxe2x80x2 is a distortion image focused by the lens with an outgoing angle of xcex8xe2x80x2. Yxe2x80x2 is an assumed true image without distortion with an angle xcex8o. The distortion aberration of the lens is defined either in terms of angle xcex2 or distance D as follows:
tan(xcex8xe2x80x2)/tan(xcex8)=xcex2xe2x80x83xe2x80x83(1)
(yxe2x80x2xe2x88x92Yxe2x80x2)/Yxe2x80x2xc2x7100=Dxe2x80x83xe2x80x83(2)
Now referring to FIG. 2, the effects of the distortion aberration are illustrated in terms of the above defined equations (1) and (2). FIG. 2A shows an original object, and FIGS. 2B and 2C respectively show an image formed by a lens which caused distortion aberration in the image. As xcex8 in equation (1) increases and xcex2 decreases, the original lattice image is distortion like a barrel as illustrated in FIG. 2C. Similarly, as D in the equation (2) is negative, the barrel image is also formed. On the other hand, as xcex8 in the equation (1) increases and xcex2 also increases, the original lattice image is distortion like a spool as illustrated in FIG. 2B.
Similarly, as D in the equation (2) is positive, the spool image is also formed. In other words, the distortion aberration of a lens causes portions of an image to be variably affected depending upon a distance from the optical center of the lens. To correct the image, certain lenses have been designed to compensate for the distortion. However, such lens design efforts are generally limited in solving the problem due to advanced features such as zooming and auto-focusing of the optical systems.
Digital processing of the images is more efficient in correcting distortion aberration than lens design efforts. One digital processing technique in correcting a distortion image is to initially determine an amount of distortion in a known image such as a lattice or a test pattern which is taken by an optical system in question. A comparison between the known image and the distortion image yields a distortion amount, and an appropriate distortion correction factor is subsequently determined. In a similar approach, a known straight line in a distortion image is selected, and the distortion line is used to determine the above described distortion amount. Another digital processing technique in correcting a distortion image involves the use of reference markers or control points on a three-dimensional object. Instead of using the above described two-dimensional lattice, the known reference markers are imaged, and the geometric relation of the markers is digitally corrected according to the known marker positions.
In the above described approaches, a series of the images must be generated with reference markers such as a lattice. In other words, the images without the reference markers are not generally suitable for digital correction of distortion. The placement of the reference markers is tedious since the image with the markers must be generated for each particular use of the lens such as a particular zoom distance. Furthermore, the marker placement is not always feasible or practical. For example, when the object is a distant scenery. Another example is old existing images which are recorded by a device that is no longer available. For these reasons, the use of reference markers is not always practical or feasible.
The distortion aberration is especially problematic for high-resolution wide angle images. Such images include panoramic images and aerial photographs. Since a series of partially overlapping images is taken and later composed into a single image, the distortion portions of the images especially near edges must be corrected prior to joining the edges of the images.
In order to solve the above and other problems, according to one aspect of the current invention, a method of correcting distortion aberration in images taken by a common optical system, includes: a) taking at least partially overlapping images of an object, the images containing a common element; b) determining correction coefficients based upon a relationship between corresponding pairs of information representing the common element in the images; and c) correcting distortion aberration in the images according to the correction coefficients.
According to a second aspect of the current invention, method of correcting distortion aberration in images taken by a common optical system, includes: j) determining a correction coefficient based upon a relationship between corresponding pairs of information on a common element in the images, the images being at least partially overlapping to contain the common element; k) correcting distortion aberration in the images according to a predetermined correction function using the correction coefficient; and l) joining the corrected images so as to generate a composed single image.
According to a third aspect of the current invention, a system for correcting distortion aberration in images, includes: an optical unit having an optical axis for focusing upon an object and generating information representing images which at least partially overlap and contain a common element of the object; a memory storage unit for storing the information; a coefficient calculation unit connected to the memory storage unit for determining correction coefficients based upon a relationship between corresponding portions of information representing the common element in the images; and an image correction unit for correcting distortion aberration in the images according to the correction coefficients.
According to a fourth aspect of the current invention,a recording apparatus for correcting distortion aberration, includes: an optical unit having an optical axis for focusing upon an object and generating information including images which at least partially overlap and contain a common element of the object, the information also including image correction data; an image storage unit connected to the optical unit for storing the images; a correction information table connected to the optical unit for containing image correction data in correcting distortion aberration in the images; and an image correction unit connected to the correction information table and the image storage unit for correcting distortion aberration in the images according to the correction data.
According to a fifth aspect of the current invention, a system for correcting distortion aberration includes: a memory storage unit for storing information representing images which at least partially overlap and contain a common element of an object; a pattern recognition unit connected to the memory storage unit for extracting a portion of the information corresponding to the common element from each of the images; and a coefficient calculation unit connected to the memory storage unit for determining correction coefficients based upon a relationship between the corresponding portions of the information representing, the correction coefficients including a first coefficient A and a second coefficient B used in the equation, f ("PHgr")=1xe2x88x92A"PHgr"2+B"PHgr"4 where "PHgr" is an angle representing the relationship of the common element in the images.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.